InAs 单量子点精细结构光谱

在5 K下,采用光致发光光谱和时间分辨光谱研究了不同单量子点的精细结构和对应发光光谱的偏振性、单激子/双激子发光光谱和相应发光动力学。给出InAs单量子点发光光谱所对应能级的精细结构及激子本征态的偏振特性。当精细结构能级劈裂为零时, 激子的本征态为简并的圆偏振态。而当精细结构能级劈裂大于零时,一般在几十到几百μeV,激子的本征态为非简并的线偏振态。相对于单激子发光寿命,激子-激子间的散射使单激子的复合发光寿命减小。

Fine-structure Spectra in InAs Single Quantum Dots

Quantum dots (QDs) samples studied in the experiment were grown by molecular-beam epitaxy on a semi-insulating GaAs substrate. It consists of an InAs QD layer embedded in the middle of a 1λ GaAs cavity. The GaAs cavity is sandwiched between a 2-period GaAs/Al_(0.9)Ga_(0.1)As distributed Bragg reflector (DBR) on top and a 20-period GaAs/Al_(0.9)Ga_(0.1)As DBR on bottom. The QD layer was formed by depositing 2.35 monolayers (ML) InAs at a growth rate of 0.001 ML/s. The sample has an ultralow density of the QDs. Therefore, we can isolate single QDs without the use of the nanoscaled masks or mesas. In the experiment the sample was cooled to 5 K and a Ti:sapphire laser operating at 750 nm was used as an excitation source. The scanning confocal microscopy with an objective (NA: 0.5) was used to spatially resolve single QDs. The photoluminescence (PL) and time-resolved PL measurements were carried out by time-correlated single-photon counting setup. The excitation light is a right circular polarization light. The polarization PL and time-resolved PL emissions were analyzed by a λ/4 and λ/2 wave plate and a linear polarizer to distinguish different polarization components. All the experiments were performed at low excitation power, which ensures the luminescence working in the single photon emission mode. The main conclusions were given: (1)Both PL peaks of the circular and linear polarization are not shifted and split and the corresponding circular (linear) polarization degree is 30% (4%).In this case, the fine-structure splitting (FSS) is close to zero and the corresponding exciton eigenstates are degenerate circular polarization states. (2)Both PL peaks of linear polarization components (π_x and π_y emissions) are splitting with the FSS of tens or hundreds of eV. In this case, the corresponding exciton eigenstates are two linear polarization states. (3)Depending on the exciton-exciton scattering, the exciton radiative recombination is modified, i.e., when there is a biexciton the decay time of the exciton decreases, compared to the case of only exciton existence at lower excitation power.